Non-invasive electromagnetic imaging has been hypothesized as an inexpensive modality for reconstructing tissue temperature distributions via differencing techniques due to strong temperature dependence of tissue electrical properties. For example, the conductivity of high water content tissues varies 1 to 2% per degrees C depending on the operating frequency used. Despite the phenomenological advantages of microwave imaging for temperature sensing, most efforts have been hampered by an inability to reconstruct quantitative images of tissue properties from which differencing techniques can be applied to estimate temperature distributions. Our current system has achieved quantitative reconstructed images of material electrical properties in laboratory scale experiments with additional tests demonstrating excellent correlation between material electrical properties and temperature in relatively simplified experimental configurations. The primary objective of t his Phase I effort will be to demonstrate the feasibility of several key aspects of an approach to realizing a clinically-viable medical microwave imaging system. Specifically, the ability to image with a fixed array transceiver system utilizing a specially-designed illumination chamber housing will be assessed. Technical success of the Phase I feasibility study will be judged on whether 1 degrees C temperature discrimination on a 1 cm spatial scale across a tissue equivalent phantom region of 30 cm in size can be achieved using the proposed methodology. PROPOSED COMMERCIAL APPLICATION: The primary application of the proposed microwave imaging system will be non-invasive monitoring of temperature field distributions during thermally-based medical procedures such as hyperthermia treatment of cancer by exploiting the strong temperature dependence of tissue electrical properties.